As is well known in the art, internal combustion engines, such as a gasoline engine, are used to drive cars or other vehicles, and the power of the reciprocating operation of the cylinders of the engines is transmitted to the wheels from one end of the crankshaft. The other end of the crankshaft is used to drive various auxiliary machinery, such as alternators, power steering and air conditioning compressors, through a pulley arrangement and one or more belts.
The crankshafts of internal combustion engines are subjected to considerable torsional vibration due to the sequential explosion of combustible gases in the cylinders. The application of forces of rotation are not smooth and continuous. Unless controlled, the vibrations can often lead to failure of the crankshaft itself, and/or also contribute to failure in other parts of the engine or cooling system, particularly where resonance occurs. The vibrations also can cause noises such as a "whine" or knocking, both of which are highly undesirable.
For many years, this problem has been recognized and a variety of devices have been constructed and used to lessen the torsional vibrations. One of the common forms of torsional damper comprises an inner metal hub attached to the end of the crankshaft, an outer metal annular member, and an elastomer member positioned between the hub and outer member. The outermost annular or ring member is often called the "inertia member". The hub directly executes the vibrations created by the crankshaft because it is rigidly coupled to it. The inertia member is coupled to the hub by the elastomer and accordingly causes a phase lag between the oscillations of the hub and the corresponding oscillations of the inertia member.
Vibration dampers of this type are disclosed, for example, in the following U.S. Pat. Nos. 2,939,338, 2,972,904, 3,479,907, 3,945,269, 4,083,265, 4,318,309, 4,378,865, and 4,395,809. Some of these patented devices relate specifically to overcoming axial shifting of the damper parts, and most are directed to the problem of overcoming torsional vibrations.
Many modes of vibration are produced by the rotating crankshaft of an engine. Torsional and bending are the two main modes of concern. Torsional vibration occurs angularly about the longitudinal axis of the crankshaft. The bending vibration mode is similar to the bending mode of a cantilevered beam. The fixed end of the crankshaft, or node, would be at some point within the engine crankcase. Conventional dynamic damping devices, such as the torsional damper devices described above, are not satisfactory to dampen or reduce such complex vibrations.
In recent years, some dual mode vibration damper devices have been proposed for the purpose of dealing with the torsional and bending vibrations associated with increased operating performance of engines. These damper devices have incorporated a pair of inertia members, a first inertia member for damping the torsional vibrations, and a second inertia member for damping the bending vibrations. The torsional vibration damper is generally of conventional construction with an annular inertia member connected to a hub through an elastomer member. The bending vibration damper comprises a second inertia member typically positioned radially inwardly of the first inertia member in an inner space of the pulley construction. The second inertia member is connected to the hub through a second elastomer member.
Dual mode damper configurations are shown, for example, in the following U.S. Pat. Nos. 4,710,152, 4,794,816, 4,815,332 and 4,881,426. These vibration damper constructions utilize two separate inertia members and two resilient elastomer members which adds additional weight to the engine and additional cost. Also, new assembly tooling and techniques are needed to construct them which adds further cost and expense.